1. Field of the Invention
The present invention relates to improvements made to sphere-type shoulder prostheses of the kind which comprise a rod which is anchored into the humeral canal and a hemispherical cup which can interact with the shoulder socket.
The prosthesis according to the invention, which may or may not be associated with a prosthetic socket, allows for the surgical treatment of degenerative afflictions of gleno-humeral arthrosis, and also of other afflictions. Furthermore, the prosthesis according to the invention is also intended for cephalo-tuberosital fractures which are not accessible to conservative surgery, and also to any painful syndrome of the shoulder.
2. Description of Background and Relevant Information
French patent application No. 2 727 002 of which the present applicant is proprietor discloses a humeral prosthesis with a sphere comprising, in the metaphyseal region of the humeral rod, a cylindrical housing with a spherical end into which a sphere designed to receive a hemispherical cup is inserted, while binding means allow these to be immobilized in a determined position with respect to the axis of the rod.
Also, French patent application No. 2 685 633 of which the applicant is proprietor discloses a modular humeral prosthesis made up of three elements one of which is an anchoring rod provided with a metaphyseal region formed of an oblique bearing face. The second element is a distance piece in the form of a wedge, one of the end faces of which fits on the bearing face of the rod. The third element of the prosthesis is a hemispherical cup, the base of which is fixed with respect to the second end face of the distance piece. This attachment, which is offcentered with respect to the geometric axis of the cup, allows for angular adjustment of the latter with respect to the distance piece.
Such prostheses have certain drawbacks regarding the systems for immobilizing the spheres, which are inaccessible once the prostheses have been inserted into the humeral canal, because the binding screws are located inside the bone cavity.
Furthermore, it can be observed that, because a sphere is being used, there are an infinite number of relative positions between rod and sphere, and this makes reproducing on the implant the geometry measured using the test piece impossible.